1. Field of the Invention
The invention relates to a method for processing binary image data (black/white representations of images) supplied from an image data supply means, such as an image scanner, before being compressed by a data compressor.
2. Prior Art
An article in NIKKEI ELECTRONICS dated Nov. 3, 1975, at pages 30-34, describes a preprocessing method for image data which is adaptable to run-length coding. In the article, black image data and white image data of a reference line and a coding line (current picture element (PELS) or scan line) are so rearranged that the black image data, i.e. black bits, are grouped into a left half of a new line and the white image data, i.e. white bits are grouped into a right half of the new line. The left half is called an A1 sequence and the right half is called an A2 sequence. Although the article relates to a preprocessing method for the image data, details of the process for the rearrangement of the image data of the article differ from that of the present invention.
The prior art preprocessing of image data such as described in the referenced article requires a complicated rearrangement of the image data for both compression and decompression processes. A simple, yet effective preprocessing system for binary image data, using a two-dimensional coding scheme for an improved compression ratio, does not presently exist.
Japanese published patent application No. 58-88970 discloses another method of preprocessing image data before supplying the image data to a compression means. The two-dimensional coding or compression scheme of CCITT is prepared for the image data of 8 PEL/MM density. The application is capable of compressing image data of other PEL density than the 8 PELS/MM by use of the compression means for the 8 PEL/MM image. If the image data has 16 PEL/MM density, the application converts the 16 PEL/MM data to the 8 PEL/MM data, and the converted data is compressed by the compression means for the 8 PEL/MM data.
Some prior art compression techniques also have the disadvantage of reducing the image quality in that an image which is compressed, then decompressed to its original resolution lacks sharpness and detail when compared to the original image. In other prior art systems, lack of effective image compression hinders data transmission (requiring greater transmission time and resources).
Accordingly, the prior art pre-processing systems for handling binary image data have undesirable disadvantages and limitations.